Comment by cjensen | Hacker News Reader

Comment by cjensen | Hacker News Reader

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It works well for Mexico, but would not be as useful in California.

Earthquake P-waves travel at 5km/s. To get 60 seconds of warning, you must be 300km (186 miles) downstream of the detector.

Mexico has a very unique situation [1]: the filled lake basins that Mexico City sits on have the same resonance frequency as buildings of a certain height. Earthquakes generate that frequency. So a serious earthquake 300km away can get the lake basin rocking, and that will knock down buildings of a certain height.

A detector is nowhere near as useful in California. Consider the Loma Prieta Earthquake. It occurred 90km from the damaged sections of San Francisco. Assuming there is a detector within 10km of Loma Prieta, that is only 16 seconds of warning. Give a few seconds for the alert to get out, and it's barely 10 seconds. That's not enough time to do anything other than hide under a desk -- which you can already do after the earthquake starts. Such a system would be excellent for bringing trains to a halt, but that's pretty much it.

[1] See preface of https://en.wikipedia.org/wiki/1985_Mexico_City_earthquake

Thanks for the explanation. However, it may be nowhere as useful, but still plenty useful. On the top of my head, 10s could be enough so:

* Trains may stop, preventing a literal train wreck.

* People doing delicate tasks (e.g., a surgeon, someone operating heavy machinery, even someone cooking) may lock to a safer position.

* Elevators may stop and open the doors safely, so no one will be stuck inside them.

* Air traffic control may hold take offs and maybe landings.

* All traffic lights going red may slightly reduce car incidents. Seems minor, I admit.

Also, people with little experience (me!) do NOT understand that an earthquake is happening until after the fact. Some blast alert even during the earthquake is very helpful for tourists and even immigrants.

Here's a video of Japan's warning system giving someone 30+ seconds of notice before the 2011 earthquake: https://www.youtube.com/watch?v=n-FMpNBfna8 (and notice how significant the shaking was, even at that distance)

Here's another example of what you can do with ten seconds: https://www.youtube.com/watch?v=gB6-nU2nJqM

Why do you suppose she props the door open with the chair? Because building shifts could jame it closed via the door frame?

Yes, there have been cases of people getting trapped in rooms/buildings due to doors getting bent or warped, so it’s common advice in Japan to prop open a door to secure yourself an exit.

That's just Triangle of Life nonsense.

https://en.wikipedia.org/wiki/Triangle_of_Life

https://www.snopes.com/fact-check/triangle-of-life/

It isn’t about buildings collapsing, it’s about doors getting stuck, so I’m not sure what relevance the Triangle of Life has here.

Those 10 seconds were staged. She knew that they were coming, she was in a small "room", and she probably took a look at her surrounding before those 10 seconds kicked and planned what to do and in which order in her head.

In real life, the warning such as this would catch people by surprise. That's not to say they wouldn't be useful, but I highly doubt they would be that useful as they were on that video.

Even if I'm in my own home, I imagine it would take me at least a fifth of that time to look around and come up with a plan of what is achievable in such a short time span.

30 seconds? you must be joking. I live in Japan and get such alerts on a regular basis. usually you get the alert about 3 to 5 seconds before the shake hits you depending on how far you are from the epicenter. If you get something 10 seconds before it hits then you dont even have to worry because it means you are very far.

* Closing natural gas and other pipeline feeds to prevent fires.

Imagine being on a tall ladder, painting, when you get the warning. Or working underneath a car on jackstands.

10 seconds would make a huge difference to some people.

Taking exceptional anecdotes under consideration is hardly useful to save lives. In reality such people should always assume that an earthquake can hit if they are in such areas at risk and use appropriate equipment.

I hate these "it wouldn't help" arguments regarding most things in this world, including this one. Case in point here, even a siren blasting 0 seconds beforehand would be useful to reduce the inevitable delay between when you feel something shaking and when you realize it's really an earthquake. I'm not sure where you're getting the idea that it wouldn't be useful, because as far as I know, the reason we don't have it is lack of funding, not lack of usefulness.

I did not way "it wouldn't help". At all.

I said that it super-helps Mexico, but that because of the specific situations in both regions, we should not anticipate getting anything like their results.

This is enough time for automated systems to have an orderly shutdown. Trains come to a stop so they don't derail. Toll both gates on bridges go down. Fire station doors open up. Elavators stop on the nearest floor and open their doors.

Given the opportunity, I know I'd rather be ten seconds further from a nearby stack of bricks or possibly-unsecured bookcase when an earthquake hits...

> Such a system would be excellent for bringing trains to a halt, but that's pretty much it.

You could also cut off gas and water lines, so it would probably prevent a lot of damage due fire or flooding.

I would bet the average time to turn off the gas line to a random house would be more than 10 minutes. Probably much more.

Automatic shutoff valves at major lines? There would still be smaller leaks where the minor lines would rupture, but the ruptures would not be continuously fed from the upstream pipes.

You could even have an automatic valve on every line.

Perhaps, but that becomes costly, fast: first on install, but especially on inspection and maintenance.

Not if the valves were automatic.

Isn't that enough time to start to slow BART trains?

They're probably already slow :)

Yes. I specifically included trains in my comment.

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